The interaction of multiple fires is a common phenomenon of combustion in forest fires. However, few available literatures examined the dual line fires on a slope. This paper constructs an experimental setup to first study the flame merging probability and flame geometry of dual parallel line fires under different slope angles (θ), heat release rates ( \(\dot {Q}\) ), and spacings (S). The flame merging probability (Pm) was found to first increase and then decrease with the increase in slope angle, which could result from the effect of upslope-induced wind. A dimensionless parameter coupling the θ, S and \(\dot {Q}\) was proposed to successfully fit the Pm. Experimental observations and analyses reveal that when Pm is large, the flame tilt angle depends on the spacing and heat release rate. Conversely, when Pm is little, the flame tilt angle is dependent on the slope angle. Accordingly, correlations of flame tilt angle were developed for Pm ≥ 0.5 and Pm < 0.5, respectively. In addition, an effective perimeter (P) coupling the burner spacing and size was proposed as the characteristic scale in the dimensionless parameter of \(\dot {Q}_{P}^{{*2/3}}{(\cos \theta )^{3/2}}\) , by which the correlation of flame height was developed for the dual parallel line fires on a slope.
